Roll over detection for an automotive vehicle

ABSTRACT

A stability control system  24  for an automotive vehicle as includes a plurality of sensors  28-37  sensing the dynamic conditions of the vehicle and a controller  26  that controls a distributed brake pressure to reduce a tire moment so the net moment of the vehicle is counter to the roll direction. The sensors include a speed sensor  30 , a lateral acceleration sensor  32 , a roll rate sensor  34 , and a yaw rate sensor  20 . The controller  26  is coupled to the speed sensor  30 , the lateral acceleration sensor  32 , the roll rate sensor  34 , the yaw rate sensor  28 . The controller  26  determines a roll angle estimate in response to lateral acceleration, roll rate, vehicle speed, and yaw rate. The controller  26  may ultimately be used to determine a tire force vector such as brake pressure distribution or a steering angle change in response to the relative roll angle estimate.

TECHNICAL FIELD

The present invention relates generally to a dynamic behavior controlapparatus for an automotive vehicle, and more specifically, to a methodand apparatus for detecting rollover of a vehicle.

BACKGROUND

Dynamic control systems for automotive vehicles have recently begun tobe offered on various products. Dynamic control systems typicallycontrol the yaw of the vehicle by controlling the braking effort at thevarious wheels of the vehicle. Yaw control systems typically compare thedesired direction of the vehicle based upon the steering wheel angle andthe direction of travel. By regulating the amount of braking at eachcorner of the vehicle, the desired direction of travel may bemaintained. Typically, the dynamic control systems do not address rollof the vehicle. For high profile vehicles in particular, it would bedesirable to control the roll over characteristic of the vehicle tomaintain the vehicle position with respect to the road. That is, it isdesirable to maintain contact of each of the four tires of the vehicleon the road.

Vehicle rollover and tilt control (or body roll) are distinguishabledynamic characteristics. Tilt control maintains the vehicle body on aplane or nearly on a plane parallel to the road surface. Roll overcontrol is maintaining the vehicle wheels on the road surface. Onesystem of tilt control system is described in U.S. Pat. No. 5,869,943.The '943 patent uses the combination of yaw control and tilt control tomaintain the vehicle body horizontal while turning. The system is usedin conjunction with the front outside wheels only. To control tilt, abrake force is applied to the front outside wheels of a turn. Oneproblem with the application of a brake force to only the front wheelsis that the cornering ability of the vehicle may be reduced. Anotherdisadvantage of the system is that the yaw control system is used totrigger the tilt control system. During certain vehicle maneuvers, thevehicle may not be in a turning or yawing condition but may be in arollover condition. Such a system does not address preventing rolloverin a vehicle.

It would therefore be desirable to provide a roll stability system thatdetects a potential rollover condition and as well as to provide asystem not dependent upon a yaw condition.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a roll controlsystem for use in a vehicle that is not dependent upon the turningcondition of the vehicle.

In one aspect of the invention, stability control system for anautomotive vehicle includes a plurality of sensors sensing the dynamicconditions of the vehicle and a controller that controls a distributedbrake pressure to reduce a tire moment so the net moment of the vehicleis counter to the roll direction. The sensors include a speed sensor, alateral acceleration sensor, a roll rate sensor, and a yaw rate sensor.A controller is coupled to the speed sensor, the lateral accelerationsensor, the roll rate sensor, the yaw rate sensor. The controllerdetermines a roll angle estimate in response to lateral acceleration,roll rate, vehicle speed, and yaw rate. The controller may also uselongitudinal acceleration and pitch rate to determine the roll angleestimate.

In a further aspect of the invention, a method of controlling rollstability of the vehicle comprises the steps of:

determining a yaw rate for the vehicle;

determining a roll rate for the vehicle;

determining a lateral acceleration for the vehicle;

determining vehicle speed; and

determining a vehicle roll rate in response to yaw rate, roll rate,lateral acceleration and vehicle speed.

One advantage of the invention is that the turning radius of the vehicleis not affected by the roll stability control.

Other objects and features of the present invention will become apparentwhen viewed in light of the detailed description of the preferredembodiment when taken in conjunction with the attached drawings andappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic rear view of a vehicle with force vectors nothaving a roll stability system according to the present invention.

FIG. 2 is a diagrammatic rear view of a vehicle with force vectorshaving a roll stability system according to the present invention.

FIG. 3 is a block diagram of a roll stability system according to thepresent invention.

FIG. 4 is a flow chart of a yaw rate determination according to thepresent invention.

FIG. 5 is a flow chart of roll rate determination according to thepresent invention.

FIG. 6 is a flow chart of a lateral acceleration determination accordingto the present invention.

FIG. 7 is a flow chart of chassis roll angle estimation andcompensation.

FIG. 8 is a flow chart of a relative roll calculation.

FIG. 9 is a flow chart of system feedback for the right side of thevehicle resulting in brake distribution force.

FIG. 10 is a flow chart of system feedback for the left side of thevehicle.

FIG. 11 is a flow chart of another embodiment similar to that of FIGS. 9and 10 resulting in change in steering position.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an automotive vehicle 10 without a rolloverstability system of the present invention is illustrated with thevarious forces and moments thereon during a rollover condition. Vehicle10 has right and left tires 12 and 13 respectively. Generally, thevehicle has a weight represented as M*g at the center of gravity of thevehicle. A gravity moment 14 acts about the center of gravity (CG) in acounter-clockwise direction. A tire moment 16 acts in a clockwisedirection about the center of gravity. Thus, the net moment 18 actingupon the vehicle is in a clockwise direction and thus increases the rollangle 20 of the vehicle. The lateral force 22 at the tire 12 on theground (tire vector) is a significant force to the left of the diagramcapable of overturning the vehicle is uncorrected.

Referring now to FIG. 2, a roll stability control system 24 is includedwithin vehicle 10, which is in a roll condition. The forces illustratedin FIG. 2 are given the same reference numerals as the forces andmoments in FIG. 1. In FIG. 2, however, roll stability controller 24reduces the tire moment 16 to provide a net moment 18 in acounter-clockwise direction. Thus, the tire vector or lateral force 22at tire 12 is reduced as well. This tendency allows the vehicle to tendtoward the horizontal and thus reduce angle 20.

Referring now to FIG. 3, roll stability control system 24 has acontroller 26 used for receiving information from a yaw rate sensor 28,a speed sensor 30, a lateral acceleration sensor 32, a roll rate sensor34, a steering angle sensor 35, a longitudinal acceleration sensor 36and a pitch rate sensor 37. Lateral acceleration and speed may beobtained using a global positioning system (GPS). Based upon inputs fromthe sensors, controller 26 controls a tire force vector by brake control38 as will be further described below or changing the steering angle.Depending on the desired sensitivity of the system and various otherfactors, not all the sensors 28-37 may be used in a commercialembodiment.

Brake control 38 controls the front right brake 40, the front left brake42, the rear left brake 44, and the right rear brake 46. Based on theinputs from sensors 28 through 34, controller 26 determines a rollcondition and controls the brake pressure of the brakes on theappropriate side of the vehicle. The braking pressure is balanced on theside of the vehicle to be controlled between the front and rear brakesto minimize the induced yaw torque and induced path deviation. The yawrate sensor 28 generates a raw yaw rate signal (YR_Raw).

Speed sensor 30 may be one of a variety of speed sensors known to thoseskilled in the art. For example, a suitable speed sensor may include asensor at every wheel that is averaged by controller 26. Preferably, thecontroller translates the wheel speeds into the speed of the vehicle.Yaw rate, steering angle, wheel speed and possibly a slip angle estimateat each wheel may be translated back to the speed of the vehicle at thecenter of gravity (V_CG). Various other algorithms are known to thoseskilled in the art. For example, if speed is determined while speedingup or braking around a corner, the lowest or highest wheel speed may benot used because of its error.

Referring now to FIG. 4, a yaw rate compensated and filtered signal(YR_CompFlt) is determined. The velocity of the vehicle at center ofgravity (V_CG), the yaw rate offset (YR_Offset) and the raw yaw ratesignal from the yaw rate sensor (YR_Raw) are used in a yaw rate offsetinitialization block 40 to determine an initial yaw rate offset. Becausethis is an iterative process, the yaw rate offset from the previouscalculation is used by yaw rate offset initialization block 40. If thevehicle is not moving as during startup, the yaw rate offset signal isthat value which results in a compensated yaw rate of zero. This yawrate offset signal helps provide an accurate reading. For example, ifthe vehicle is at rest, the yaw rate signal should be zero. However, ifthe vehicle is reading a yaw rate value then that yaw rate value is usedas the yaw rate offset. The yaw rate offset signal along with the rawyaw rate signal is used in the anti-windup logic block 42. Theanti-windup logic block 42 is used to cancel drift in the yaw ratesignal. The yaw rate signal may have drift over time due to temperatureor other environmental factors. The anti-windup logic block also helpscompensate for when the vehicle is traveling constantly in a turn for arelatively long period. The anti-windup logic block 42 generates eithera positive compensation OK signal (Pos Comp OK) or a negativecompensation OK signal (Neg Comp OK). Positive and negative in thismanner have been arbitrarily chosen to be the right and left directionwith respect to the forward direction of the vehicle, respectively. Thepositive compensation OK signal, the negative compensation OK signal andthe yaw rate offset signal are inputs to yaw rate offset compensationlogic block 44.

The yaw rate offset compensation logic block 44 is used to take dataover a long period of time. The data over time should have an averageyaw of zero. This calculation may be done over a number of minutes. Ayaw rate offset signal is generated by yaw rate offset compensationlogic 44. A summing block 44 sums the raw yaw rate signal and the yawrate offset signal to obtain a yaw rate compensated signal (YR_Comp).

A low pass filter 48 is used to filter the yaw rate compensated signalfor noise. A suitable cutoff frequency for low pass filter 48 is 20 Hz.

Referring now to FIG. 5, a roll rate compensated and filtered signal(RR_CompFlt). The roll rate compensated and filtered signal is generatedin a similar manner to that described above with respect to yaw rate. Aroll rate offset initialization block 50 receives the velocity at centerof gravity signal and a roll rate offset signal. The roll rate offsetsignal is generated from a previous iteration. Like the yaw rate, whenthe vehicle is at rest such as during startup, the roll rate offsetsignal is zero.

A roll rate offset compensation logic block 52 receives the initializedroll rate offset signal. The roll rate offset compensation logicgenerates a roll rate offset signal which is combined with the roll rateraw signal obtained from the roll rate sensor in a summing block 54. Aroll rate compensated signal (RR_Comp) is generated. The roll ratecompensated signal is filtered in low pass filter 56 to obtain the rollrate compensated and filtered signal that will be used in latercalculations.

Referring now to FIG. 6, the raw lateral acceleration signal (Lat AccRaw) is obtained from lateral acceleration sensor 32. The raw lateralacceleration signal is filtered by a low pass filter to obtain thefiltered lateral acceleration signal (Lat Acc Flt). The filter, forexample, may be a 20 Hz low pass filter.

Referring now to FIG. 7, a roll angle estimation signal (RollAngleEst)is determined by chassis roll estimation and compensation procedure 62.Block 64 is used to obtain a longitudinal vehicle speed estimation atthe center of gravity of the vehicle. Various signals are used todetermine the longitudinal vehicle speed at the center of gravityincluding the velocity of the vehicle at center of gravity determined ina previous loop, the compensated and filtered yaw rate signal determinedin FIG. 4, the steering angle, the body slip angle, the front left wheelspeed, the front right wheel speed, the rear left wheel speed, and therear right wheel speed.

The new velocity of the center of gravity of the vehicle is an input tobody roll angle initialization block 66. Other inputs to body roll angleinitialization block 66 include roll angle estimate from the previousloop and a filtered lateral acceleration signal derived in FIG. 6. Anupdated roll angle estimate is obtained from body roll angleinitialization. The updated roll angle estimate, the compensation andfiltered roll rate determination from FIG. 5, and the time of the loopis used in body roll angle integration block 68. The updated roll angleestimate is equal to the loop time multiplied by the compensated andfiltered roll rate which is added to the previous roll angle estimateobtained in block 66. The updated roll angle estimate is an input toroll angle estimate offset compensation block 70.

The velocity at the center of gravity of the vehicle is also an input toinstantaneous roll angle reference block 72. Other inputs toinstantaneous roll angle reference block 72 include the compensated andfiltered yaw rate from FIG. 4 and the filtered lateral accelerationsignal from FIG. 6. The following formula is used to determine areference roll angle:

Reference Roll Angle=ARCSin [1/g(VCG*YRCompFlt-LatAccFlt)]

Where g is the gravitational constant 9.81 m/s² The reference roll anglefrom block 72 is also an input to roll angle estimate offsetcompensation. The updated roll angle estimation is given by the formula:${RollAngleEst} = {{{RollAngleEst}\quad \left( {{from}\quad {Block}\quad 68} \right)} + {\left( {{ReferenceRollAngle} - {{RollAngleEst}\left( {{Block}\quad 68} \right)}} \right)\frac{{loop}\quad {time}}{Tau}}}$

Where Tau is a time constant and may be a function of steering velocity,LatAcc and V-CG. A suitable time constant may, for example, be 30seconds.

Referring now to FIG. 8, a relative roll angle estimation(RelativeRollAngleEst) and a road bank angle estimate signal isdetermined. The first step of the relative roll angle calculationinvolves is the determination of road bank angle compensation timeconstant (Tau) block 72. The velocity at the center of gravity, thesteering velocity and the filtered lateral acceleration signal from FIG.6 are used as inputs. A compensated and filtered roll rate (RR_CompFlt)is used as an input to a differentiator 74 to determine the rollacceleration (Roll Acc). Differentiator 74 takes the difference betweenthe compensated and filtered roll rate signal from the previous loop andthe compensated and filtered roll rate from the current loop divided bythe loop time to attain the roll acceleration. The roll accelerationsignal is coupled to a low pass filter 76. The filtered rollacceleration signal (Roll Acc Flt), roll angle estimate, the filteredlateral acceleration signal and the loop time are coupled to chassisrelative roll observer block 78. The chassis roll observer 78 determinesthe model roll angle estimation (Model Roll Angle Est). The model rollangle is a stable estimation of the roll dynamics of the vehicle whichallows the estimates to converge to a stable condition over time.

From the model roll angle estimation from block 78, the initial relativeroll angle estimation from block 72, a road bank angle initializationfrom a block 79 loop time and a roll angle estimate, road bank anglecompensation block 80 determines a new road bank angle estimate. Theformula for road bank angle is:${RoadBankAngleEst} = {\frac{{Loop}\quad {Time}}{{TauRoad}_{—}{Bank}}*\left( {{RollAngleEst} - \begin{pmatrix}{{ModelRollAngle} +} \\{RoadBankAngleEst}\end{pmatrix}} \right)}$

The roll angle estimate may be summed with the road bank angle estimatefrom block 80 in summer 82 to obtain a relative roll angle estimate. Theroad bank angle estimate may be used by other dynamic control systems.

Referring now to FIG. 9, the relative roll angle estimate from FIG. 8and a relative roll deadband are summed in summer 84 to obtain an upperroll error. The upper roll error is amplified in KP_Roll Amplifier 86and is coupled to summer 88. The roll rate compensated and filteredsignal from FIG. 5 is coupled to KD_Roll Amplifier 90. The amplifiedroll rate signal is coupled to summer 88. The filtered roll accelerationsignal from block 8 is coupled to KDD_Roll Amplifier 82. The amplifiedsignal is also coupled to summer 88. The proportioned sum of theamplified signals is the right side braking force effort. From this, theright side brake force distribution calculation block 94 is used todetermine the distribution of brake pressure between the front and rearwheels. The front right normal load estimate and the rear right normalload estimate are inputs to block 94. The front right roll controldesired pressure and the right rear roll control desire pressure areoutputs of block 94. The block 94 proportions the pressure between thefront right and rear right signals to prevent roll. The front right, forexample, is proportional according to the following formula:${{FR}\quad {desired}\quad {pressure}} = {{Right}\quad {side}\quad {braking}\quad {effort}\quad \left( \frac{{FR}{Normal}}{{FR} + {RR}} \right)}$

The output of block 94 is used by the brake controller of FIG. 3 toapply brake pressure to the front right and rear right wheels. The brakecontroller factors in inputs such as the brake pressure currentlyapplied to the vehicle through the application of pressure by the driveron the brake pedal. Other inputs include inputs from other dynamiccontrol systems such as a yaw control system.

Referring now to FIG. 10, a similar calculation to that of FIG. 9 isperformed for the left side of the vehicle. The relative roll angleestimate and relative roll deadband are inputs to summing block 96.However, the signs are changed to reflect that the left side of thevehicle is a negative side of the vehicle. Therefore, relative rollangle estimate and relative roll deadband are purely summed together 96in summing block 96 to obtain the lower roll error. The lower roll erroris passed through KP_Roll amplifier 98. The compensated and filteredroll rate is passed through KD_Roll amplifier 100 and the filtered rollacceleration signal is passed through KDD_Roll amplifier 102. Theinverse of the signals from amplifiers 98, 100 and 102 are input andsummed in summer 104 to obtain the left side braking effort.

A left side brake force distribution calculation block 106 receives theleft side braking effort from summer 104. The front left normal loadestimate and the rear left normal load estimate. In a similar manner tothat above, the front left and rear left roll control brake pressuresare determined. By properly applying the brakes to the vehicle, the tiremoment is reduced and the net moment of the vehicle is counter to a rolldirection to reduce the roll angle and maintain the vehicle in ahorizontal plane.

Referring now to FIG. 11, a change in steering angle may be effectuatedrather than or in combination with a change in brake force distribution.In either case, however, the tire force vector is changed. In FIG. 11,the same reference numerals as those in FIGS. 9 and 10 are used but areprimed. Everything prior to blocks 88′ and 104′ is identical. Blocks 88′and 104′ determine right side steering effort and left side steeringeffort, respectively.

The right side steering effort is placed through a clamping circuit 108to ensure that a positive value is obtained. The left side steeringeffort is likewise placed through a clamping circuit 110 to ensure apositive value is obtained.

A summing block 112 receives the output from circuits 198 and 110 wherethe right side is negative and the left side is positive. A deltasteering angle is obtained from block 112. The method of FIG. 11 isparticularly suited for drive-by-wire systems or other systems thatallow the steering angle to be directly controlled. The delta steeringangle is an amount that changes the tire force vector to counteractroll. The delta steering angle can be used to directly move the wheelsof the vehicle to physically change the direction of steering.

If both steering and brake distribution are used controller 26 will beused to apportion the amount of correction provided by steering andbrake Addistribution. The amount of apportionment will depend on theroll rate and other variables for the particular vehicle. The amount ofapportionment will thus be determined for each vehicle. For example,higher profile vehicles will be apportioned differently from a lowprofile vehicle.

As described above the longitudinal acceleration sensor and a pitch ratesensor may be incorporated into the above tire force vectordetermination. These sensors may be used as a verification as well as anintegral part of the calculations. For example, the pitch rate or thelongitudinal acceleration or both can be used to construct a vehiclepitch angle estimate. This estimate along with its derivative can beused to improve the calculation of the vehicle roll angle. An example ofhow the rate of change of the vehicle roll angle using theses variablesmay be constructed is:

 GlobalRR≈RRComp_Flt+PitchRateCompFlt(−YawRate+Sin(GlobalRollAngleEst)*Tan(VehiclePitchAngleEst))+(YawRateCompFlt*Cos(GlobaMR)*Tan(PitchAngleEst))

Where PitchRateCompFlt is a compensated and filtered pitch rate signal,GlobalRollAngleEst is an estimated global roll angle,VehiclePitchAngleEst is an estimated vehicle pitch angle estimate, andGlobalRR is a global roll rate signal. Of course, those skilled in theart may vary the above based upon various other factors depending on theparticular system needs.

While particular embodiments of the invention have been shown anddescribed, numerous variations and alternate embodiments will occur tothose skilled in the art. Accordingly, it is intended that the inventionbe limited only in terms of the appended claims.

What is claimed is:
 1. A rollover detection system for a vehiclerollover comprising: a speed sensor; a lateral acceleration sensor; aroll rate sensor; a yaw rate sensor; and a controller coupled to saidspeed sensor, said lateral acceleration sensor, said roll rate sensor,said yaw rate sensor, said controller determining a roll angle estimatein response to lateral acceleration, roll rate, vehicle speed, and yawrate, said controller determining, roll rate in response to a raw rollrate signal and a roll rate offset.
 2. A system as recited in claim 1further comprising a sensor selected from the group of a steering anglesensor, a longitudinal acceleration sensor and a pitch rate sensor.
 3. Asystem as recited in claim 2 wherein said controller determines vehiclespeed at a center of gravity of the vehicle in response to said steeringangle and said steering sensor.
 4. A method of determining roll over ofa vehicle comprising: determining a yaw rate for the vehicle;determining a roll rate for the vehicle in response to a raw roll ratesignal and a roll rate offset; determining a lateral acceleration forthe vehicle; determining vehicle speed; and determining a vehicle rollrate in response to yaw rate, roll rate, lateral acceleration andvehicle speed.
 5. A method of determining roll over of a vehiclecomprising: determining a yaw rate for the vehicle in response to a yawrate signal and a yaw rate offset; determining a roll rate for thevehicle; determining a lateral acceleration for the vehicle; determiningvehicle speed; and determining a vehicle roll rate in response to yawrate, roll rate, lateral acceleration and vehicle speed.
 6. A method asrecited in claim 4 further comprising the step of determining vehiclespeed at the center of gravity of the vehicle as a function of a frontright wheel speed, a rear right wheel speed, a front left wheel speed, arear left wheel speed, and a steering wheel angle.
 7. A method ofdetermining roll over of a vehicle comprising: determining a yaw ratefar the vehicle; determining a roll rate for the vehicle; determining alateral acceleration for the vehicle; determining vehicle speed at thecenter of gravity of the vehicle as a function of body slip angle; anddetermining a vehicle roll rate in response to yaw rate, roll rate,lateral acceleration and vehicle speed.
 8. A rollover detection systemfor a vehicle rollover comprising; a speed sensor; a lateralacceleration sensor; a roll rate sensor; a yaw rate sensor, a steeringangle sensor; a longitudinal acceleration sensor; a pitch rate sensor;and a controller coupled to said speed sensor, said lateral accelerationsensor, said roll rate sensor, said yaw rate sensor, a steering anglesensor, a longitudinal acceleration sensor and a pitch rate sensor, saidcontroller determining a roll angle estimate in response to lateralacceleration, roll rate, vehicle speed, yaw rate, steering angle,longitudinal acceleration and pitch rate, said controller determiningroll rate in response to a raw roll rate signal and a roll rate offset.9. A system as recited in claim 8 wherein said controller determinesvehicle speed at a center of gravity of the vehicle in response to saidsteering angle and said steering sensor.